In some applications, such as the display of radar data on a television mode scanner screen, the data is supplied in a coordinates system (polar in this example) which is not the system of the display device (Cartesian coordinates in the case of television scanning). Therefore, it is necessary to proceed to a coordinates conversion. In the previous example, this function is carried out by a DSC.
However, when the conversion and/or display process is quantified, as is the case for a DSC and its television display, it can happen that the conversion causes the appearance of dark patches in a luminous zone (in the case of a television display), as explained in detail below (FIG. 2). This gives an uneven appearance to the image. It is thus desirable to smooth the image at this level by "filling" the dark patches, i.e. by conferring thereupon a non-zero luminosity. This defect correction process is known as "pixel filling".
In the framework of the DSC, one solution is known. It will be recalled that a DSC comprises a memory, called image memory, that stores the image to be displayed on the screen, a certain number of bits of this memory being attributed to each of the dots or pixels of the screen considered as distinct. The solution consists in attributing to the pixels not addressed by the conversion, thus dark, a non-zero luminosity value which is a function of luminosity of the adjacent pixels, for example that of the eight pixels which surround the pixel involved. This solution rapidly encounters limits and restrictions, associated essentially to its complexity and to costs incurred, when the processing rates must be high such as is often the case for a radar.
An object of the invention is to provide a method for pixel filling which is not reached by the conversion and which is earlier to perform than the known solution.
According to the invention, this filling is performed not at the level of the pixels of the image memory, but at the level of the signal received in polar coordinates (modulus .rho., polar angle .theta.). If the video signal (amplitude as a function of .rho.) corresponding to a given value of angle .theta. is called "radial", the method thus consists in creating artificial radials between the effective or real radials and in attributing to each of them a video signal which is a function of the video signal of the adjacent effective radials. These artificial radials are thereafter converted into Cartesian coordinates and fill the pixels not previously filled.